US soldiers check for land mines and IEDs on a canal running through Highway 1 on the outskirts of Kandalay village in Kandahar province. Photograph: Romeo Gacad/AFP/Getty Images

Scroll through the list of Britain's dead in Afghanistan and time after time the cause of death is low-tech bombs made with fertiliser and a little know-how.

About 70% of Nato casualties have been due to improvised explosive devices and last year there were a record number of makeshift IEDs .

In the regional command of which Helmand is part, the number of IEDs jumped 13% between 2010 and 2011, despite attempts to smash the networks of insurgents manufacturing, distributing and planting the bombs.

That probably reflects the effect of the US "surge" of troops into the province in 2010, which pushed the Taliban onto the back foot and forced them to rely ever more on the deadly weapons.

"It's a great device to use against a conventional force," said Doug Czarnecki, deputy commander of Task Force Paladin, which counters the IED threat. "The insurgent can't fight that with conventional which means they have got to find something to attack."

Insurgents have been able to get hold of fertiliser without difficulty, turn it into bombs and move across the very porous border between Afghanistan and Pakistan. The US is trying to find ways to alter chemical fertilisers made in Pakistan so they are harder to turn into explosives. In Helmand, where most British troops are based, a higher than average number of IEDs are detonated by the weight of the victim who unwittingly stands on them.

Not only has there been a remorseless rise in the number of devices pouring out of backroom bomb factories, the insurgents have become ever more adept at making them more lethal.

"When we come up with measures to defeat their tactics, they change them," said Czarnecki. "When we introduce new counter-measures they change again."

When extra armour was added to vehicles the insurgents responded with bigger bombs. Then, when radio jamming equipment was introduced to foil remote control detonation, the rebels increased their use of command wires.

But the development that makes the bombs so difficult to counteract is the emergence of IEDs containing only tiny quantities of metal. They now tend to have no metal shrapnel, relying instead on damage caused by rocks surrounding the explosive hurtling into the body of the person who sets off the bomb. Metal triggers have also been abandoned. That means traditional metal detectors used to find buried bombs are largely useless.

Troops have responded with what officials call "better tactics and training". British troops arriving in Helmand will spend at least two weeks training at Camp Bastion before being sent out to the forward operating bases (FoBs). At Bastion there is a purpose-built training area that should help them identify in different types of terrain whether an IED has been planted . It will be drilled into them that little things really count – telltale clues of where to look, and what to look out for.

Better still, the troops will be told they need to build relationships with villagers, who may know where IEDs are hidden.

In recent months, within the three districts where the British are operating, commanders have come to rely upon this type of intelligence. If the villagers aren't talking to you, watch which routes they are using – and which ones they are avoiding too.

The constant need for vigilance makes the work of patrolling the villages of southern Afghanistan incredibly arduous, but it seems to be paying off. Despite the increasing number of IEDs, the number of casualties caused by the bombs in the military region that includes Helmand declined by 20% between 2010 and 2011, officials said.

Another factor has been the speed and quality of treatment given to troops wounded in IED blasts.

The medical emergency response teams that fly from Camp Bastion have saved countless lives, not least because they take consultants out with them in adapted Chinook helicopters.

Specialist treatment begins as soon as the helicopter lands, not when the patient gets back to the operating theatre.

Many British troops badly injured in Afghanistan choose to have amputations even when their limbs can be saved, because recovery can be quicker and less painful.

Some soldiers who have lost their legs can be running within six weeks, while those with supposedly less severe wounds can need multiple operations over months before any improvement.

An estimated 300 troops have had amputations in the past decade, and 3,000 more need help with serious long-term injuries.